EP4105174A1 - Poudre de nitrure d'aluminium et sa méthode de production - Google Patents

Poudre de nitrure d'aluminium et sa méthode de production Download PDF

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EP4105174A1
EP4105174A1 EP21753929.5A EP21753929A EP4105174A1 EP 4105174 A1 EP4105174 A1 EP 4105174A1 EP 21753929 A EP21753929 A EP 21753929A EP 4105174 A1 EP4105174 A1 EP 4105174A1
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aluminum nitride
powder
nitride powder
surface area
specific surface
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German (de)
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EP4105174A4 (fr
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Yoshinori Tagashira
Yoshiaki Yamashita
Masato Hamamoto
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Tokuyama Corp
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Tokuyama Corp
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Definitions

  • the present invention relates to an aluminum nitride powder useful as a raw material when an aluminum nitride sintered body excellent as an insulating high thermal conductive member is manufactured, particularly, by press molding, and a method for manufacturing the aluminum nitride powder.
  • the aluminum nitride sintered body is widely used as a heat dissipation material or an electric insulation material for applications such as a heat dissipation substrate of an electric device, an electronic circuit board, and a member for a semiconductor manufacturing apparatus by taking advantage of high thermal conductivity and a high insulation property which are characteristics of aluminum nitride.
  • One method for manufacturing the aluminum nitride sintered body is a method for molding an aluminum nitride powder into a granular shape, then press-molding the granular aluminum nitride powder, and heat-sintering the press-molded product ( JP 3479160 B2 ).
  • the granular aluminum nitride powder is generally manufactured by mixing the aluminum nitride powder with a solvent and furthermore, appropriately, a binder to prepare a slurry, and granulating the slurry by spray drying ( JP 2525074 B2 ).
  • the aluminum nitride powder obtained by the reduction-nitridation method includes spherical primary particles and have a favorable filling property, but includes many slightly sintered aggregated particles due to heat during reduction-nitridation, and cannot achieve a high bulk density. Therefore, pulverization has been performed in order to reduce the aggregated particles.
  • an aluminum nitride powder containing a carbon powder taken out from a reduction-nitridation furnace is pulverized ( JP H2-102109 A , JP H5-17109 A , JP H5-43209 A , and JP H4-265208 A ).
  • a pulverizer such as a dry ball mill or pin mill ( JP 2005-162555 A ).
  • the present inventors made intensive studies, and as a result, have found that as for a raw material for manufacturing aluminum nitride granules to be used for press molding, the bulk density of the aluminum nitride granules can be increased by disintegration to such an extent that large aggregated particles are crushed without strongly pulverizing the aluminum nitride powder containing a carbon powder taken out from a reduction-nitridation furnace.
  • the present inventors have found that, according to the above disintegrating, the specific surface area of the aluminum nitride powder does not become extremely high, an increase in the oxidation amount in a subsequent oxidation treatment for decarburization (also referred to as decarburization treatment) is also suppressed, and an effect of preventing a decrease in thermal conductivity is also exhibited.
  • a treatment with an ejector is particularly effective as the disintegrating means.
  • the present inventors have found that it is possible to provide an aluminum nitride powder having predetermined characteristics which has not been conventionally provided, and have completed the present invention.
  • the configuration of the present invention is as follows.
  • the aluminum nitride powder of the present invention has a characteristic that primary particles thereof have a high sphericity by adopting a reduction-nitridation method.
  • an aluminum nitride powder obtained by performing the disintegration treatment an aluminum nitride powder having a specific particle size distribution in which a shoulder due to coarse particles disappears and a peak top portion increases in a particle size distribution curve as compared with a particle size distribution of an aluminum nitride powder manufactured without performing the treatment can be obtained.
  • an increase in the specific surface area after the treatment as compared with that before the treatment is suppressed to be low.
  • the aluminum nitride powder having such characteristics achieves a high pressurized bulk density, and granules obtained by using the aluminum nitride powder have a high bulk density. Therefore, high thermal conductivity and strength can be imparted to a sintered body obtained by press-molding the granules.
  • the aluminum nitride powder of the present invention has a smaller amount of oxygen and can provide a sintered body having higher thermal conductivity in combination with the particle size distribution than an aluminum nitride powder obtained by performing a disintegration treatment.
  • An aluminum nitride powder according to the present invention includes primary particles having a sphericity of 0.8 or more, preferably 0.9 or more. That is, in the aluminum nitride powder according to the present invention, the particle shapes of the primary particles are uniform in a spherical shape. The characteristics of the shape of the aluminum nitride powder can be confirmed by observation with a SEM photograph.
  • a median size D 50 obtained by a laser diffraction method is 0.5 to 1.5 ⁇ m, preferably 0.8 to 1.3 ⁇ m, and a ratio D 90 /D 50 of a particle size D 90 corresponding to a cumulative undersize distribution of 90% to the D 50 is 2.2 or less, preferably 2.0 or less.
  • the aluminum nitride powder having such a value of D 90 /D 50 has a sharp particle size distribution and has uniform particle shape, and therefore has a high pressurized bulk density. A shrinkage ratio of a molded body using the aluminum nitride powder after firing is highly suppressed. Therefore, an aluminum nitride sintered body having excellent dimensional accuracy and effectively reduced warpage and distortion can be obtained.
  • the aluminum nitride powder has a BET specific surface area of 2 to 4 m 2 /g, preferably 2 to 3 m 2 /g, and a total oxygen concentration of 0.6 to 1.2% by mass.
  • the total oxygen concentration is increased by a mechanochemical effect.
  • a powder having a total oxygen concentration within the above range indicates that the powder is not subjected to a large impact. Even at this total oxygen content, sintering proceeds sufficiently, and a sintered body excellent in physical properties such as thermal conductivity can be obtained.
  • the degree of aggregation calculated from the median size D 50 and the BET specific surface area by the following formula is within a range of 1.1 to 2.2, preferably within a range of 1.3 to 2.0. Since the aluminum nitride powder of the present invention has a low degree of aggregation, granules which have high dispersibility in, for example, a resin or a solvent, and are easily crushed can be manufactured.
  • a method for manufacturing such an aluminum nitride powder according to the present invention is not particularly limited, but for example, the aluminum nitride powder can be manufactured by the following manufacturing method.
  • a synthetic powder containing aluminum nitride aggregated particles and a carbon powder obtained by reducing and nitriding a raw material powder containing an aluminum oxide powder and a carbon powder under nitrogen is disintegrated without using a medium, and then excess carbon is oxidized and removed.
  • a mixed powder of an alumina powder and a carbon powder is caused to react at 1400 to 1700°C for two to ten hours in an atmosphere containing nitrogen by a reduction-nitridation method to synthesize an aluminum nitride powder.
  • the median size is 0.15 ⁇ m or more and 1.5 ⁇ m or less, and preferably 0.5 ⁇ m or more and 1.2 ⁇ m or less.
  • the raw material carbon powder is not particularly limited, and examples thereof include acetylene black, channel black, furnace black, and graphite powder. Among these, acetylene black is preferable from a viewpoint of higher purity.
  • the specific surface area of the carbon powder is not particularly limited, but is preferably 0.01 to 500 m 2 /g.
  • a method for mixing and dispersing the alumina powder and the carbon powder may be any known method, and is not particularly limited, but for example, various mixers such as a ball mill can be used.
  • the raw material powder is nitrided at 1400°C to 1700°C under a nitrogen atmosphere. Nitridation is performed by a usual method until the raw material powder is completely nitrided.
  • a carbon powder having a reaction equivalent or more to the alumina powder is usually used.
  • a mixing ratio between the alumina powder and the carbon powder is preferably within a range of 3.5 to 5.0 in terms of carbon/alumina molar ratio. When the molar ratio is less than 3.5, alumina that has not reacted remains. On the other hand, when the molar ratio is too large, cost for removing carbon is increased, which is not economical.
  • a synthetic powder obtained by the reduction-nitridation reaction generally 5 to 30% by mass, particularly about 10 to 20% by mass of carbon remains.
  • a disintegrating means not using a medium such as balls or beads, specifically, for example, a treatment with an ejector, a treatment with a Laval nozzle, or a treatment with a jet mill.
  • a treatment with an ejector capable of performing disintegrating using acceleration of an air flow and a shear flow is suitably adopted from viewpoints that an effect can be obtained by a simple apparatus and generation of a fine powder at the time of disintegrating is suppressed as much as possible to stabilize the quality.
  • the pressure of a compressed gas (generally air) supplied to the ejector is 0.1 to 1 MPa, preferably 0.2 to 0.7 MPa, and the concentration of the synthetic powder to be treated in an air flow is 1.00 kg/m 3 or less, preferably 0.02 to 0.60 kg/m 3 at normal pressure.
  • a compressed gas generally air
  • the specific surface area of the synthetic powder furthermore, the specific surface area of an aluminum nitride powder finally obtained by decarburizing the synthetic powder has a change ratio of 10% or less, which is extremely small, between the specific surface area before disintegrating and the specific surface area after disintegrating.
  • D50 and D10 of the aluminum nitride powder finally obtained have a small change between the treated particles and the untreated particles.
  • D10 is a particle size corresponding to a cumulative undersize distribution with 10%.
  • D90 is decreased by the treatment, and a predetermined particle size ratio of the present invention is satisfied.
  • the synthetic powder after the disintegration treatment contains excess carbon powder as described above, by performing a decarburization treatment, an aluminum nitride powder can be obtained.
  • a known method for burning excess carbon powder using an oxidizing gas at a high temperature is adopted without particular limitation.
  • any gas that can oxidize carbon such as air or oxygen
  • air is suitable in consideration of economic efficiency and the oxygen content of aluminum nitride to be obtained.
  • a treatment temperature is preferably 500 to 1100°C, and more preferably 600 to 900°C in consideration of decarburization efficiency and excessive oxidation of an aluminum nitride surface.
  • Time for the decarburization treatment only needs to be appropriately set according to the degree of reduction in carbon. However, for example, when the decarburization treatment is performed at 600 to 900°C, the time for the decarburization treatment is one to six hours.
  • an apparatus including a transfer device (also referred to as a hopper) for transferring a nitrided synthetic powder to a disintegrating means, a disintegrating means disposed below the hopper, and a collecting means for collecting a disintegrated powder, as illustrated in Fig. 1 , is used.
  • a transfer device also referred to as a hopper
  • a disintegrating means disposed below the hopper
  • a collecting means for collecting a disintegrated powder
  • a known hopper can be adopted without particular limitation, and a hopper having a container shape such as a conical shape or an inverted quadrangular pyramid shape is suitably used because a powder is hardly retained at a bottom due to the shape.
  • An outlet of the hopper is connected to a disintegrating means such that the synthetic powder can be introduced into the disintegrating means.
  • a disintegrating means a disintegrating means not using a medium such as an ejector as described above is suitably adopted.
  • the disintegrated synthetic powder is collected by a collecting means such as a bag filter through a pipe and then sent to an oxidation step.
  • disintegrating can be performed simultaneously with transport of the synthetic powder, and the disintegration treatment can be performed very advantageously in an industrial view.
  • the aluminum nitride powder obtained by the present invention can be suitably used, for example, as a raw material for manufacturing a sintered body.
  • the aluminum nitride powder is processed into, for example, aluminum nitride granules as a raw material for press molding or a sheet molded body by a known method, it is possible to obtain a sintered body in which a shrinkage ratio is highly suppressed, dimensional accuracy is excellent, and warpage and distortion are effectively reduced.
  • a method for manufacturing the aluminum nitride granules will be specifically exemplified.
  • a known sintering aid that can be used for sintering aluminum nitride for example, an alkaline earth metal oxide such as calcium oxide or strontium oxide, a rare earth oxide such as yttrium oxide or lanthanum oxide, or a composite oxide such as calcium aluminate, is mixed within such a range that the ratio of the sintering aid to the total amount of the aluminum nitride powder and the sintering aid is 0.1 to 10% by mass, and the resulting mixture is molded into a granular form.
  • an alkaline earth metal oxide such as calcium oxide or strontium oxide
  • a rare earth oxide such as yttrium oxide or lanthanum oxide
  • a composite oxide such as calcium aluminate
  • the aluminum nitride granules may contain, for example, a surface active agent, a binder, a lubricant, or a plasticizer containing an organic component as necessary.
  • the surface active agent is generally used for enhancing dispersibility of a ceramic powder in a slurry, and a known surface active agent is adopted without any limitation as the surface active agent of the present invention.
  • a surface active agent having a hydrophilic-lipophilic balance hereinafter, abbreviated as HLB
  • HLB hydrophilic-lipophilic balance
  • HLB is a value calculated by the Davis formula.
  • the surface active agent that can be suitably used include carboxylated trioxyethylene tridecyl ether, diglycerin monooleate, diglycerin monostearate, carboxylated heptaoxyethylene tridecyl ether, tetraglycerin monooleate, hexaglycerin monooleate, polyoxyethylene sorbitan monolaurate, and polyoxyethylene sorbitan monooleate. Two or more kinds of surface active agents may be mixed and used.
  • These surface active agents are usually selected and used within a range of 0.01 to 10 parts by mass, preferably 0.02 to 3.0 parts by mass with respect to 100 parts by mass of the aluminum nitride powder.
  • the amount of the surface active agent is less than 0.01 parts by mass, dispersion of the slurry is insufficient, and when the amount of the surface active agent is more than 10 parts by mass, the strength of the molded body decreases, which is not preferable.
  • a binder generally used for molding a ceramic powder can be used without any limitation.
  • organic polymers such as oxygen-containing organic polymers such as polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, poly 2-ethylhexyl methacrylate, polybutyl methacrylate, polyacrylate, cellulose acetate butyrate, nitrocellulose, methyl cellulose, hydroxymethyl cellulose, polyvinyl alcohol, polyoxyethylene oxide, and polypropylene oxide; hydrocarbon-based synthetic resins such as a petroleum resin, polyethylene, polypropylene, and polystyrene; polyvinyl chloride; and a wax and an emulsion thereof are used.
  • organic polymers such as oxygen-containing organic polymers such as polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, poly 2-ethylhexyl methacrylate, polybutyl methacrylate, polyacrylate, cellulose acetate but
  • the molecular weight of the organic polymer used as the binder is not particularly limited, but in general, when an organic polymer having a molecular weight of 3,000 to 1,000,000, preferably 5,000 to 300,000 is used, the density of an aluminum nitride powder molded body obtained by press molding increases, which is preferable.
  • a ratio of the binder with respect to 100 parts by mass of the aluminum nitride is preferably 0.1 to 30 parts by mass.
  • the ratio is less than the above range, it is difficult to mold a favorable molded body due to insufficient strength.
  • the ratio is more than the above range, the physical properties of an aluminum nitride sintered body obtained by press-molding and firing the aluminum nitride granules tend to deteriorate.
  • a lubricant for enhancing pressure transmission during press molding or a plasticizer for enhancing collapsibility of granules may be used at a ratio of 5 parts by mass or less with respect to 100 parts by mass of the aluminum nitride powder.
  • an organic solvent preferably used for manufacturing granules for example, one kind or a mixture of two or more kinds selected from ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alcohols such as ethanol, propanol, and butanol; aromatic hydrocarbons such as benzene, toluene, and xylene; esters such as ethyl acetate and butyl acetate; and halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene, and bromochloromethane are used.
  • the amount of the organic solvent is selected and used from a range of 20 to 200 parts by mass with respect to 100 parts by mass of aluminum nitride.
  • the above-described components are mixed and formed into a slurry, and then the slurry is formed into aluminum nitride granules by a known granulation method such as a spray dryer method.
  • the aluminum nitride granules are formed into a press-molded body by a so-called dry press method in which the aluminum nitride granules are filled in a predetermined molding die and pressurized by a press molding machine.
  • the aluminum nitride powder obtained by the present invention is used as a raw material, by selectively disintegrating and reducing large aggregated particles of the aluminum nitride powder, a pressurized bulk density can be increased. As a result, a filling property during press molding can be improved, the bulk density of a press-molded body, consequently the sintering density of a sintered body to be obtained can be sufficiently increased, and an aluminum nitride sintered body having further improved thermal conductivity can be obtained.
  • Each particle size was determined by dispersing aluminum nitride powder in a sodium pyrophosphate aqueous solution with a homogenizer, and performing measurement by a laser diffraction method using MICROTRAC HRA manufactured by MicrotracBEL Corp.
  • the specific surface area of an aluminum nitride powder was measured by a BET method using a fluidized surface area automatic measuring device Flow Sorb 2300 manufactured by Shimadzu Corporation.
  • the total oxygen content in an aluminum nitride powder was measured using an in-ceramic oxygen-nitrogen analyzer EMGA -620W manufactured by HORIBA, Ltd.
  • the pressurized bulk density of an aluminum nitride powder was determined by preparing a pellet having a diameter of 20 mm and a thickness of 2.0 mm at a pressing pressure of 200 kg/cm 2 , and measuring the size and mass of the pellet.
  • the sphericity of an aluminum nitride powder was determined by selecting 100 arbitrary particles from a photographic image of an electron microscope, measuring the major axis and minor axis of each of the particle images using a scale, and averaging values of (minor axis)/(major axis).
  • 280 g of ⁇ -alumina having an average particle size of 1.0 ⁇ m and a specific surface area of 6 m 2 /g and 140g of carbon black having a specific surface area of 110 m 2 /g were mixed for two hours with a dry vibration ball mill, and then nitrided at a firing temperature of 1600°C for firing time of ten hours in a nitrogen atmosphere to obtain a synthetic powder.
  • the obtained synthetic powder was supplied from the hopper of the apparatus illustrated in Fig. 1 with an ejector using compressed air at 0.3 MPa such that the concentration of the synthetic powder at normal pressure was 0.3 kg/Nm 3 , and treated to be disintegrated.
  • the treated aluminum nitride powder was sent to a bag filter through a pipe and collected, and then decarburized at 650°C for three hours under an air atmosphere in a container with a stirring function equipped with a heater to obtain an aluminum nitride powder.
  • Example 1 As Comparative Example 1, the synthetic powder of Example 1 not subjected to the disintegration treatment was decarburized under similar conditions.
  • the specific surface area, the pressurized bulk density, D 10 , D 50 , and D 90 , the total oxygen content, and the particle size distribution of each of the aluminum nitride powder of Example 1 subjected to the decarburization treatment after the disintegration treatment and the aluminum nitride powder of Comparative Example 1 obtained by decarburizing the synthetic powder not subjected to the disintegration treatment were measured. Results thereof are indicated in Table 1 and Fig. 2 . In addition, the sphericity of each powder was 0.9 or more.
  • 280 g of ⁇ -alumina having an average particle size of 1.0 ⁇ m and a specific surface area of 6 m 2 /g and 140g of carbon black having a specific surface area of 110 m 2 /g were mixed for two hours with a dry vibration ball mill, and then nitrided at a firing temperature of 1700°C for firing time of ten hours in a nitrogen atmosphere to obtain a synthetic powder.
  • the synthetic powder not subjected to the disintegration treatment was decarburized to obtain an aluminum nitride powder.
  • the specific surface area, D 10 , D 50 , and D 90 , total oxygen content, and pressurized bulk density of the obtained aluminum nitride powder were measured, and results thereof are indicated in Table 1.
  • An aluminum nitride powder was obtained in a similar manner to Example 1 except that the disintegrating conditions of the synthetic powder with the ejector were changed as indicated in Table 1.
  • the specific surface area, D 10 , D 50 , and D 90 , total oxygen content, and pressurized bulk density of the obtained aluminum nitride powder were measured, and results thereof are indicated in Table 1.
  • the synthetic powder obtained in Comparative Example 2 was disintegrated in a similar manner to Example 1, and then decarburized similarly to obtain an aluminum nitride powder.
  • the specific surface area, D 10 , D 50 , and D 90 , total oxygen content, and pressurized bulk density of the obtained aluminum nitride powder were measured, and results thereof are indicated in Table 1.
  • shrinkage ratio indicated in Table 1 is an average value of shrinkage ratios obtained by preparing ten sintered bodies for each aluminum nitride powder and calculating the shrinkage ratios of the sintered bodies.
  • Shrinkage ratio % L 0 ⁇ L s ⁇ 100 / L 0
  • Fig. 2 illustrating the particle size distribution of an obtained aluminum nitride powder indicates that the shoulder portion on the large particle side in Comparative Example 1 has disappeared by the disintegration treatment and the rising angle of the particle size distribution curve is sharp, and D 90 /D 50 of the aluminum nitride powder of Comparative Example 1 obtained without performing the disintegration treatment of the present invention was 2.4, whereas D 90 /D 50 of the aluminum nitride powder of Example 1 obtained by performing the disintegration treatment of the present invention was 1.8.

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